The DRAM half pitch is predicted to become less than 20 nm if the technology follows the scaling trend according to the ITRS road map reports. As a consequence, providing a patterned semiconductor chip with a minimal feature size below 20 nm is a matter of great importance in field of lithography. Extreme Ultraviolet lithography (EUV) with a wavelength of 13.5-14 nm had been proposed as one option for reaching the 10 nm technology node. However, the generation of the EUV source involves plasma reaction and extreme vacuum that are both high in cost and not production ready. EUV light source intensity is currently at least one or two orders of magnitude lower than the conventional lithography light intensity. In addition, moving to EUV means the challenge of using reflective masks and researching a completely different etching chemistry. In order to overcome the weak EUV power problem, improvements on the sensitivity of the resist had been raised. Nevertheless, a highly sensitive resist generates shot noise that results in significant sidewall roughness.
Maskless, massively parallel electron beam lithography (EBL) is an EUV alternative and another way to advance to the next technology node. The many variants of EBL essentially eliminate the mask and use tens or hundreds of thousands of electron beams to do the etching. Compared to EUV, EBL is a straightforward alternative but has been hindered by low throughput. Thus, the massively parallelizing EBL still requires more improvements before the process can become profitable.
Without the help of EUV and EBL, other approaches such as using a special material and photoresist chemical reaction had been demonstrated to be effective for a sub 20 nm feature formation. The above-mentioned chemical based patterning approach includes treating a hard-baked resist pattern with a material effective enough to make an alkaline surface of the resist pattern; applying a second layer of a second photosensitive composition to be in contact with the alkaline surface of the resist pattern, wherein the second photosensitive composition comprises a second resin component and a photoacid generator; exposing the second layer to activating radiation; and developing the exposed second layer to form spacers over the layers to be patterned, wherein the spacers comprise portions of the second layer not removed during the second layer development.
It is the cross-linked reaction between the alkaline surface and the second layer that contribute to the formation of spacers. The spacers are then used as a soft mask with a smaller feature size, thereby patterning the underlying layers to be patterned. Due to the fact that the occurrence of the chemical reaction is essential to the present procedure, the materials used to form each features is limited to a certain category, mostly soft materials, which is problematic when a higher processing temperature is required.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.